The present invention relates to a screen taking-up device for taking up and unrolling a screen--any of various types, e.g., curtains, blinds, light weight shutters, tents, movie screens, etc.--which is done by driving its take-up shaft in the normal and reverse directions.
When taking up or unrolling the screen wound on the aforementioned take-up shaft by the driving force of a motor, this operation is simplified, if the screen is automatically stopped at a specified taken-up position or an unrolled position merely by a single operation of a motor driving switch.
The stopping of the screen at a specified position as above-described is made possible by providing a positioning mechanism for controlling the motor to stop, as the amount of movement of the screen is found to have reached the value preset for making the stop, as counted by a counter, for example.
If the inertial output of the motor acts on the screen, however, the screen does not stop at the preset stop position, but it overruns the stop position, making it impossible to have correct stop position, even if the motor is controlled to stop, when the screen is being unrolled, for example.
On the other hand, a method considered effective for eliminating the inertial output of the motor is that with an electromagnetic brake provided on the output side of the motor, brake is applied on the inertial output by switching this electromagnetic brake on in sync with the stop control timing of the motor.
However, this condition involves the problem of power consumption increase, because the electromagnetic brake must be energized while the screen is stopped at the taken-up position or the unrolled position.
Another problem is that even with a construction adapted for operation of the screen by the driving force of a motor, as above-described, if the device is so composed as to permit the operation of the screen in manual way, the operation of the screen is interrupted or operation of small amount of taking-up-unrolling of the screen is desired to make, but if the manual output is simply connected to the take-up shaft, the motor is rotated by this manual output, thus interfering with the revolution of the take-up shaft.